Telephone system



June 27, 1939. Q w HALUGAN 2,164,033

TELEPHONE SYSTEM Filed Jan. 8, 1938 2 Sheets-Sheet 1 A k I V &

l I l i I L) 2 w v B wwww ATTORNEY June 27, 1939. c. w. HALLIGAN TELEPHONE SYSTEM Filed Jan. 8 1958 2 Sheets-Sheet 2 l/V VE N 7' OR c. WHA LL/GAN A 7' TOR/VE V l?atented June 27, 1939 PATENT OFFlCE TELEPHONE SYSTEM Clair W..Halligan, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 8, 1938, Serial No. 183,978

8 Claims.

This invention relates to telephone systems and particularly to systems having multi station subscribers lines.

The objects of the invention are to facilitate the making of a simple and positive test of a line to identify the calling station thereon; to enable the testing of the stations for identification and the operation of the station bells over metallic circuits from the central office that are free from grounded connections at the substations; to prevent the speech-transmission circuits from interfering with the discriminating identification tests; and to effect other improvements in systems of this character.

Numerous systems have been devised heretofore for making discriminating tests of calling party lines to determine which party on the line has initiated the call. The usual purpose of these tests is to enable the selective operation of the subscribers message registers to charge the different parties for the calls they make. It has generally been found necessary in these prior systems to employ grounded connections at the substations, either for the circuits over which the tests are made, or for the signaling circuits, or .for both testing and signaling.

1 According to the present invention, however, the disadvantages of these prior systems have beenovercome by means of a party-line arrangement in which the substations are tested, to identify them when calling, and the bells at these substations are rung, when the subscribers are being called, over a full-metallic circuit from the central office, eliminating the use of any grounded connections at the subscribers premises.

, The stations on the line are distinguished by directional conducting devices, such as discharge tubes. For a two-party line the tube at each station is included in a bridge across the line, while the station is in a calling condition, to permit the how of test current when the test source of relatively high potential and of the proper polarity is applied to the line from the central office. The discrimination is made possible by the fact that the tubes are oppositely poled in their respective -test bridges. And, while the test bridge is in parallel with the substation talking transmission bridge, which is also closed when the station is in a calling condition, the test bridge does not interfere with transmission since the discharge tube therein is non-conductive at the relatively low talking-current potentials. Since, however, the talking transmission bridge is of necessity non-directional, allowing current to pass through it in either direction, and since it is connected in parallel relation to the test bridge at the time the identification test is made,

it would act as a shunt and would destroy the distinguishing character of the test bridge unless some provision were otherwise made to avoid this shunting effect. This is accomplished by including in the transmission bridge at the substation a resistor element which has a normal resistance suificiently high to prevent this bridge from acting as a shunt on the test bridge, and which lowers its resistance markedly in response to the application of potential from the centraloffice battery for an appreciable interval of time. And, to insure that this resistor is in its highresistance state at the instant the test is made, the central-office battery is first disconnected from the line for an interval long enough to permit the resistor to assume its normal, high resistance. Then the test is made through the test bridge, following which the central-oifice battery is reconnected to the line, and the resistor again lowers its resistance to put the transmission bridge in condition for conversation. Thus the parallel transmission bridge is "automatically given a high-resistance value during the brief interval the identification test is being made.

According to a further feature of the invention the signal bell is connected in series with the directional discharge tube in a bridge across the line so that the directional character of the tube makes it possible to selectively ring the substation bell by sending ringing current of proper polarity over the conductors of the line in series.

Other features of the invention will become ap parent from the following description and also from the appended claims.

In the drawings accompanying the description:

Fig. 1 discloses a two-party subscribers line having discriminating means at the stations to enable the identifying tests;

Fig. 2 discloses part of the central office equipment for making connections with the subscribers lines, for signaling the stations, and for making the identification test of the stations on the line; and

Fig.3 shows a modification of the substation circuits on the party line. 50

The party line I is equipped with twostations PI and P2, each of which is provided with the usual transmitter, receiver, dial, induction coil, and ringer Besides these elements the stations are also provided with directional devices; such55 as gas-filled tubes, and with variable resistance elements.

At station Pl, for example, the discharge tube 2 is connected in series with the bell 3 and the variable resistor 4 in a bridge circuit across the conductors 5 and 6 of the line i. The gas-filled tube 2, which may be of any well-known construction, has three electrodes and is designed to pass current in one direction only when the applied voltage is of suflicient magnitude to cause ionization. This tube is so connected in the bridge circuit at station PI that is passes current when the positive pole of the source is connected to conductor 6 and the negative pole to conductor 5 of the line.

The variable resistance element 4, included in the bridge with the tube 2 and the ringer 3, is preferably of some material such as silver sulphide or boron or uranium oxide, having a high negative temperature coefiicient of resistance. The normal resistance of these elements is so high that no appreciable current can flow upon the application of potential thereto. However, they become heated after the potential has been applied for an appreciable interval and greatly lower their resistance, thereby permitting the flow of increased current through the circuit.

The station PI is also equipped with a second one of these variable resistance elements 7. The element "4 is included with the winding of induction coil 8, the transmitter 9 and the contacts of dial I0 in the transmission and control bridge across the conductors of the line I.

It will be noted that the bridge circuit including the tube 2 and the bridge including the transmitter 9, dial I6, and resistor l are in parallel relation with each other when the receiver I I is off the hook. Since the transmission and control bridge is necessarily of comparatively low resistance when the transmitter is energized, this bridge would act as a shunt on the bridge including the tube 2, thus making it impossible to make use of the directional character of the tube for testing the identity of the station. To avoid this difficulty the resistor 1 is placed in the transmission bridge. When no current is flowing, this resistor has a high-resistance value, but as soon as current from the central ofiice battery flows through the transmission bridge to energize the transmitter 9 the element lowers its resistance, due to the heating efiect of the current, to place said bridge in condition for controlling the cen tral oifice equipment and also in condition for speech transmission.

The station P2 is similar to station PI, except that the tube I2 is poled in the opposite direction in the bridge including the ringer I3 and resistor I4. The second resistor I5 at station P2 is similarly connected in the transmission and control bridge including a winding of the induction coil I'6, transmitter I? and contacts of dial I8.

The party line I terminates at the central office in the bank of a line finder F and also in the bank of a connector switch C. The finder switch F is joined by a message register link circuit to the brushes of a first selector switch S. These switches may be of any suitable type. They are illustrated diagrammatically in the drawings, and much of the equipment of the link circuit connecting the finder and selector has been omitted for the sake of simplicity. These message register link circuits are in general well known in the art, and reference is made, for a better understanding of their detailed operation,

to the patent to Hovland 1,823,688 of September 15, 1931.

The operation of the system will now be described, and for this purpose it will be assumed first that the party at station PI initiates a call. When the receiver II is removed from the switchhook, a circuit is closed from battery through the winding of line relay I9, contact of cut-01f relay 2|], thence over conductor 6, variable resistor I, induction coil winding 8, closed contacts of the switchhook, transmitter 9, contacts of dial I6, and returning over line conductor 5 through the contact of relay 20 and the other winding of relay I9 to ground. This circuit includes the transmission and control bridge at the station PI, and at the instant the switch hook contacts are closed this bridge is in a high-resistance state due to the normal high-resistance value of the element I. However, the element 1 shortly reduces its resistance to a low value, al-

lowing full current to flow over the line and through the transmission bridge at the calling station. Relay I9 at the central office operates and causes the line finder F to hunt and seize the calling line I in the well-known manner. As soon as the finder F seizes the line, the cut-off relay 20 is operated, and the line relay is disconnected. The conductors of the line I are now extended through the link circuit and the windings of the battery supply relay 2| associated with the first selector switch S. Current continues to fiow over the line I from the central-ofiice battery through the windings of the relay 2|, and the element I is maintained at its low-resistance value.

The potential of the central-office battery is also applied to the discharge tube 2 over the test bridge, which extends from line conductor 5 through the tube 2, resistance 49, thence through the closed contacts 22 of the switchhook to the other conductor 6. It will be noted that the switchhook contacts 22 open the circuit of the ringer 3 and its associated resistor 4 when the station is in a calling condition and close the test bridge, including the tube 2 and resistance 49 directly across the conductors of the line. ever, the potential of the central oflice battery is insufiicient to cause the tube 2 to ionize; consequently no current flows through the test branch at this time.

The transmission and control bridge at the calling station being in its low-resistance state due to the low-resistance value of the element 1, the subscriber may now proceed to operate this dial II] to set the selector switch S and succeeding switches to extend his line to the desired called line. At some suitable time during the establishment of the connection the message register circuit performs a test of the calling line to identify the calling station thereon. This test may be made as soon as the calling line is extended through the line finder to the message register circuit, it may be performed between the dialing of successive digits, or it may be made after the digits have been dialed. When the time arrives for making the identification test, a circuit is closed for the operation of relay 23. The relay 23 in operating disconnects the centralofiice battery from the conductors of the line I and closes an energizing circuit for relay 24, which is slow to attract its armatures. As soon as relay 24 closes its front contacts the two conductors of the line I are extended through the windings of polarized test relays 25 and 26 and the contacts of relay 2'! to the high-potential test battery 28, However, during the interval that Howrelay 24 is attracting its armatures, the line I is entirely disconnected from any source of potential, and the resistor l at the calling station, being deprived of heating current, immediately assumes its normal high-resistance condition. When, therefore, relay 24 finally closes its front contacts to apply the high-potential test battery 28 to the line, the transmission and control bridge at the substation PI is in its high-resistance condition, and no appreciable current is permitted to flow from the battery 28 through the transmission bridge.

Since the test bridge including the tube 2 is also closed across the line at this time, the high potential of battery 28 is applied to the electrodes of the tube 2. The circuit for this purpose may be traced from the negative pole of battery 28 to the lower norm al contact of relay 2?, winding of polarized relay 25, contact of relay 24, contact of relay 23 through the finder switch F over the line conductor 6, switchhook contacts 22, resistance 49, to the anode and to the control electrode of the tube 2. The circuit may be further followed from the cathode of the tube 2 over the other line conductor 5 through the line finder and the upper front contact of relay 23, contact of relay 24, winding of polarized relay 2% and the upper normal contact of relay 2? to ground. Thetube 2 is poled to pass current when the positive potential of the test source is connected to the conductor 6; hence no current flows over the circuit traced, and neither of the polarized test relays 25 and 2'6 operates.

At the time relay 24 operates it closes a circuit for the slow-operate relay 21. After sufficient time has been measured to perform the first test of the line, relay 21 operates and reverses the connections of the test battery 28. The negative pole of battery 28 is then connected to the line conductor 5 and the positive pole thereof is connected to conductor 6. Accordingly the tube 2 ionizes and passes current through the test bridge at the calling station and through the windings of the test relays 25 and 26 at the central oflice. The polarized relays 25 and 26 are connected in opposite directions in the test circuits, the relay 26 operating and the relay 25 remaining deenerglzed. Relay 26 closes an obvious circuit for the register relay 29, which operates and locks to the control conductor 30. As soon as the second test has been completed the relay "231s permitted to release, disconnecting the test battery 28 from the line and reconnecting the conductors of the line through the windings of relay 2| to the central-office talking and control battery.

The application of the test battery 28 first in one direction and then in the other direction to the conductors of the line has no efiect on the bridge, the combinedresistance of the ringer l3 acts as a shunt on the test bridge including the tube 2. has been completed and the central-oflice battery reconnected to the line I, the element 1 again lowers its resistance and restores the transmission and control bridge to its operative condition. The establishment of the connection may now be completed, if this has not already been done before the test is made; and the subscribers may converse with each other.

At the end of conversation the subscribers replace their receivers on the switchhooks, and the release of the central-ofiice equipment is initiated. At some convenient time during the process of release and while the line finder F is still in connection with the terminals of the line I, the relay 32 is operated in the. message register link circuit. Relay 32 closes the metering circuit from the positive pole of battery 33 through the lamp 34 and resistance 35, contact of relay 32, closed contact of relay'29, which identifies the calling station PI, conductor 36 through the line finder F, inner right contact of relay through the winding of the message register 31, individual to the calling station Pl. Register 31 operates and charges the call to the station Pl. Thereafter the release of the equipment proceeds, and the line finder F and the message register link circuit are fully restored to normal.

When a call is. made by the party at station P2, the operation of the equipment is substantially the same as that already described. The only difference is that the identification tests result in the ionization of the tube I2at station P2 when the positive pole of the battery 28 is connected to the line conductor 5. Accordingly the polarized relay operates and relay 26 remains deenergized. Relay 25 operates thev register relay 38, whichlccks to the control conductor 30. At the end of conversation the message register operating circuit is closed through the left contact of relay 38, conductor 39 through the line finder F and the winding of the message register 40 to battery. The message register 40 operates and charges the call to the station P2.

Assume now that call is extended to the line I by way of the connector switch C, and assume further that the party at station PI is wanted. After the connector C has tested and seized the line, it applies selective ringing current from the polarized source 4| to the line in the direction to ionize the tube 2 at station Pl. As soon as the tube 2 becomes ionized, the potential of the ringing source is applied to the ringer 3 and the resistance element 4, the switchhook contacts 22 being in their normal position at this time. The applied potential causes the element 4 to lower its resistance to permit the full flow of ringing current through the ringer 3. The bell of the ringer 3 is sounded to attract the attention of the called party. In a similar manner the party at station P2 may be signaled by applying signaling current of the opposite polarity to the line I.

The party line illustrated in Fig. 3 is similar to the one shown in Fig. 1, except for differences in the ringing circuits. is connected between the conductor 43 and ground over a ringing circuit. that extends through the tube 44 and a closed contact of the switchhook. This means that the party at station P3 is signaled by connecting the negative pole of the ringing current source to the conductor 43, the returnv circuit for the ringing current being by way ofthe grounded connection. When the. subscriber. at station P3linitiatesa call the receiver switchhook disconnects the ringer 42 However, after the identification test The ringer 42 at station P3 from the line and closes the identification test bridge including the tube 44 and resistance 50 directly across the two conductors of the line. This tube passes test current when the positive pole ofthe source is connected to the conductor 47 and the negative pole is connected to conductor 43. As in the case of Fig. 1, the removal of the receiver from the switchhook also closes the transmission and control brige, including the variable resistor 45, across the line conductors.

The circuits at station P4 are the same as those at station P3, except that the tube 46 is poled to pass ringing current when the negative pole of the source is connected to the line conductor 41. The tube 46 passes identification test current when the positive pole of the test current source is connected to conductor 43 and the negative pole to conductor 41.

What is claimed is:

1. The combination in a telephone system of a subscribers line having a substation thereon, a test bridge at the substation, a transmission bridge at said substation, means controlled by the subscribers switchhook for closing both of said bridges in parallel across the conductors of said line when the subscriber initiates a call, a variable resistor in the transmission bridge having a high resistance when no current is flowing and a low resistance when current is flowing therein, a source for feeding transmission current over said line and through said transmission bridge, means for temporarily disconnecting said source of current from the line to permit said variable resistor to assume its high-resistance value, a source of test potential, and means for applying said test potential source to said test bridge while said source of transmission current is disconnected from the line.

2. The combination in a telephone system of a subscribers line having a substation thereon, a circuit branch at said substation for making identification tests, a second circuit branch at said substation for transmission and control purposes, means operative when the subscriber initiates a call for connecting both of said branches to said line in parallel relation with each other, a source for feeding current over said line through said transmission and control branch, a variable resistance element in said second branch having a high resistance when no current is flowing and a low resistance when current is flowing through said second branch, a source of test potential, means for disconnecting said first-mentioned source from said line to allow said resistance element to assume its high-resistance value, and means for applying said source of test potential to the line to cause test current to flow through said test branch while said element is in its highresistance condition.

3. The combination in a telephone system of a subscribers line having a plurality of stations thereon, each one of said stations having a circuit branch for making identification tests and a circuit branch for talking transmission, each of said test branches having a conducting device therein for distinguishing the corresponding station from other stations, each of said transmission branches including a variable resistor having a, high resistance when no current is flowing and a low resistance when current is flowing through the transmission branch, means controlled by the switchhook of a calling one of said stations for connecting both of said circuit branches in parallel across the conductors of said line, a source of transmission current, and means for connecting the same to said line to cause the flow of current over the line and through the transmission branch at the calling station, means fordisconnecting said transmission source momentarily to permit the resistor at the calling station to assume its high-resistance value, a source of test potential, and means for connecting said test potential source to the test bridge at the calling station while the resistor thereat is in its high-resistance condition.

4. The combination in a telephone system of a subscribers line having a plurality of stations thereon, each station having a circuit branch for making identification tests and a circuit branch for talking transmission, each test branch having a directional discharge device therein for identifying the corresponding station, each transmission branch having a normally high-resistance element therein, means controlled by he switchhook at the station of a calling party for closing both the test branch and the transmission branch in parallel across the conductors of said line, a source of potential for supplying talking current to said line, means for applying the potential of said source to the transmission branch at the calling station, the resistance element in said transmission branch responding to the application of potential thereto by lowering its resistance to permit the flow of current through said transmission branch, means for temporarily disconnecting said source from the line to permit said resistance element to restore to its highresistance condition, a source of test potential, and effective while the resistance element at the calling station is in its high-resistance state applying said test potential source to the directional discharge device in the test branch of the calling station to identify said station.

5. The combination in a telephone system of a subscribers line having a plurality of stations thereon, each station having a directional discharge device and a ringer included in a bridge across the conductors of said line, a source of polarized ringing current, means for connecting the same to said line to send ringing current to the stations over a circuit including both conductors of the line, the directional discharge device at each station being poled to permit the flow of ringing current of a corresponding polarity through the corresponding ringer, each station having a transmission branch including a normally high-resistance element, means controlled by the switchhook at a calling station for closing the transmission branch and for closing in parallel therewith a test branch including the directional discharge device and excluding the ringer, a source of talking current and means for connecting the same to the transmission branch at the calling station, the resistance element in said branch responding by lowering its resistance to permit the flow of talking current through said transmission branch, the directional discharge device in the parallel test branch being non-responsive to the potential of said talking current source, means for temporarily disconnecting the talking current source from said line to allow the resistance element at the calling station to assume its high-resistance state, a source of test potential, and means effective while said resistance element is in its high-resistance state for connecting said source of test potential to the test bridge at the calling station to identify said station.

6. The combination in a telephone system of a subscribers line having a plurality of stations ing an identification test current in a series cir cuit including the two conductors of said line and the identification bridge at any particular one of said stations to identify such station.

7. The combination in a telephone system of a subscribers line having a plurality of stations thereon, each station having a ringer connected in a ringing bridge free from all ground connections across the conductors of said line, each station having an identification bridge free from all ground connections and means for connecting the same across the conductors of said line, each station having a directional current conducting device connected in a common portion of both the ringing and identification bridges, means for applying signaling current of different polarities in a circuit including thetwo conductors of said line and said ringing bridge in series to operate selectively the ringer at any station, and means for applying test currents of different polarities in a series circuit including the two conductors of said line and the identification bridge at any particular one of said stations toidentify such station.

8. The combination in a telephone system. of a subscribers line having a plurality of stations thereon, each station having a ringer connected in a ringing bridge free from all ground connections across the conductors of said line when the station is in a non-calling condition, each station having a microphone connected in a transmission bridge across the conductors of said line when said station is in a calling condition, each station having an identification bridge free from all ground connections and means for connecting the same across the conductors of said line in parallel with said transmission bridge when the station is in a calling condition, means for applying signaling current in a circuit including the two conductors of said line and said ringing bridge in series to operate selectively the ringer at any station, means for applying an identification test current in a series circuit including the two conductors of said line and the identification bridge at any particular one of said stations to identify such station, and means for preventing said transmission bridge from interfering with said identification bridge when test current is being applied to said line.

CLAIR W. HALLIGAN. 

